Conventional chain lubricants for low temperature applications are usually mineral oil based for cost reasons. Chain lubricants for higher temperature applications, e.g. where the chain passes through an oven, may be polyol ester based lubricant to prolong the periods between lubricant replenishment and to minimize the amount of deposits on the chain surfaces due to oxidation. Inadequate lubrication causes chain wear and increased operational costs due to increased energy consumption. Inadequate lubrication can be from lack of lubricant or from a lubricant of insufficient viscosity to maintain a lubricious film of sufficient thickness. The build up of oxidation products on chains may require chain cleaning and or replacement.
Chain lubricants desirably have low volatility, retain fairly constant viscosity over the life of the lubricant, and do not form sludge or varnish on the chain due to oxidation or other degradation reactions. Volatility is usually associated with both the vaporization and the breakdown of the lubricant into lower molecular weight volatile components. Sludge and/or varnish formation is usually associated with molecular weight build-up due to the polymerization of degraded lubricant molecules.
While conventional mineral oil based lubricants for chains work well at 100° C. and even slightly higher, elevated temperatures tend to volatilize the mineral oil and cause oxidation reactions that form sludge deposits on the chain. Addition of more oil can compensate for evaporation, but the formation of deposits generally requires cleaning the chain with a varnish remover product. Depending on the length of the chain, the complexity of the chain and associated hardware to carry the part, and the complexity of the equipment, which the chain passes through, the chain cleaning can be quite complicated and expensive. Further the solvents necessary for effective varnish removal tend to be regulated as environmental hazards in terms of worker exposure and recycling or discarding.
Polyol esters have better thermal and oxidative stability than mineral oil but are several times more expensive than mineral oils. Polyol esters however have some affinity for water, which water can promote cleavage of the ester bonds yielding carboxylic acids and half esters. The carboxylic acids can contribute to metal corrosion. Polyol esters are preferred over mineral oils for higher temperature applications such as above 125, 150 or 180° C.